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Hydrogen: The Future Fuel

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Hydrogen: The Future Fuel

David Pacchioli, Dana Bauer, Emily Wiley

June 08, 2005

Beyond petroleum

Is hydrogen the answer?

"I will get right to the point," declared Nobel laureate Richard Smalley, speaking before Congress. "Energy is the single most important problem facing humanity today. We must find an alternative to oil. We need to somehow provide clean, abundant, low-cost energy to the six billion people that live on the planet today, and the 10-plus billion that are expected by the middle of this century."

Smalley has a philosophical ally in Bruce Logan, Kappe professor of environmental engineering and director of Penn State's Hydrogen Energy Center. "When U.S. oil production peaked 30 years ago, demand exceeded output and the result was an oil crisis," Logan reminds us. "But when global oil production peaks, in the next ten to twenty years, we'll have another, more serious, crisis."

The race for solutions is on, and while ideas may diverge, the parameters are clear: The new energy source must be cheap, renewable, and environmentally clean. Non-polluting hydrogen—energy-dense and the most abundant element in nature—meets two of these requirements in spades. But whether it can be produced and used inexpensively is the crux of a large and growing effort in research, in the U.S. and abroad.

"It can't happen without breakthroughs," Logan acknowledges. "We need cheaper and better materials" in every facet of development—for the catalysts and membranes that make up fuel cells; for the safe, efficient storage of hydrogen aboard vehicles; for the solar cells that will be key to hydrogen production. Another significant challenge is to develop the necessary infrastructure for hydrogen delivery.

Under the umbrella of the Hydrogen Energy Center, Penn State researchers are working on all these problems, ranging from fundamental materials chemistry to collaborations with Pennsylvania's growing fuel-cell industry.

Though their goal may be thirty years away, Logan and his colleagues are clear about one thing: "The time to lay the groundwork is now."

We're pleased to offer our readers a glimpse at their future-building activities.

Energy Unbound

Hydrogen is all around us. But how do we get at it?

If you were a science-fiction writer trying to dream up the perfect fuel, you could hardly do better than hydrogen. High in energy, it produces almost no pollution when burned. It's also the simplest and most abundant of elements, making up 90 percent of all matter. It's present in stars and living things, in fossil fuels and, most tantalizingly of all, in water.

"Water will be the coal of the future," Jules Verne wrote with confidence in 1874. But Verne didn't have to reckon with the challenges of extraction.

Today, almost all hydrogen is produced via steam reforming of natural gas at oil refineries like this Conoco plant near Denver, Colorado.

Warren Gretz (DOE/NREL)

Today, almost all hydrogen is produced via steam reforming of natural gas at oil refineries like this Conoco plant near Denver, Colorado.

As it happens, hydrogen doesn't like to be alone. Hydrogen molecules—each composed of a pair of atoms, or H2, are always eager to bind with other molecules—with oxygen, with carbon, with almost every element.

Hydrogen may be everywhere, in other words, but it isn't floating free. In order to be used as fuel, hydrogen has to be removed from its attachments. And that removal requires energy.

Cracking hydrocarbons

Today, almost all the world's hydrogen is produced by "reforming" fossil fuels. "You can react any hydrocarbon source with steam and the products are carbon monoxide and hydrogen," explains Harold Schobert, professor of fuel science and director of the Energy Institute at Penn State. "Usually there's an easy way to convert the carbon monoxide to carbon dioxide, and then you can separate that, and you're left with fairly pure hydrogen."

Worldwide, according to the U.S. Department of Energy, some 48 percent of hydrogen is currently produced from natural gas, 30 percent from oil, and 18 percent from coal. The remaining four percent is produced from water.

Fossil-fuel reforming has definite advantages. The process is well-understood and relatively cheap. Yet producing hydogen this way still creates carbon dioxide emissions, contributes to global warming, and does nothing to reduce our dependence on foreign oil.

Even with these drawbacks, many experts suggest that fossil-fuel reforming will be an important transitional step in the long haul toward a hydrogen economy. In the U.S, there is particular interest in coal gasification as an attractive interim option, due to plentiful and relatively inexpensive coal reserves. he carbon dioxide produced by reforming could be piped underground instead of released into the atmosphere, some experts have suggested.

Harold Schobert is not convinced that coal gasification is a good idea even as a short-term strategy. "Don't get me wrong," he says. "I love coal. But when you talk about gasification, plus shifting the gas composition, plus CO2 capture, plus sequestration—all those processes require energy. And if you're going to do carbon sequestration, why stack the deck against yourself by starting with the highest carbon material?" Even natural gas reforming, Schobert suggests, may be a questionable goal. "Here's a material that's already a premium fuel, it's the cleanest burning hydrocarbon there is, it has the highest thermal energy, it's easy to transport and store. Why go to a lot of work to make it into another clean burning high-energy gas?"Maybe it makes more sense," he adds, "just to use natural gas until the technologies for extracting hydrogen from renewable sources are solid enough to take over."

Leslie Eudy (DOE/NREL)

Photovoltaic array used for solar-powered electrolysis to produce hydrogen for fuel-cell buses at SunLine Transit Agency in Thousand Palms, California.

Splitting water

Chief among these renewable sources is plain old water. By passing an electric current through H2O, you can split the aqueous molecule neatly into its constituent elements. Hydrogen gas rises from the negative cathode, and oxygen gas collects at the positive anode. The process is called electrolysis, and it's been around since Jules Verne's time.

Electrolysis produces a very pure form of hydrogen and it's simple enough to be widely adapted. Some futurists envision an electrolysis box in every garage, producing hydrogen from tap water.

The catch is that electrolysis requires electricity. Lots of it. And if that electricity is being produced in the conventional fashion—from fossil fuels—then again we're just running in place in terms of producing clean energy.

Light-scattering layer

We do, of course, have a renewable source for all the electricity we could possibly want: It mounts the sky every morning. Yet whilethere has been considerable progress in solar technology over the last twenty years, researchers still haven't figured out how to harness the sun's power cost-efficiently.

Courtesy Tom Mallouk

Scanning electron microscope (SEM) image of a titanium dioxide "inverse opal" grown in Tom Mallouk's laboratory at Penn State. Writes Mallouk: "The titanium dioxide honeycomb scatters light very strongly in the red part of the visible spectrum. A layer of this stuff improves the efficiency of dye-sensitized solar cells by directing light that would otherwise pass through the cell to the dye molecules.

It's easy to see how improving solar cells is a critical step towards an affordable hydrogen economy.What we need," says Tom Mallouk, "is good cheap materials that do what a solar cell already does pretty well."

Mallouk is Dupont professor of materials chemistry and physics, and director of Penn State's Center for Nanoscale Science. As he explains it, today's best solar cells are reasonably efficient, converting sunlight to electricity at a rate of about 25 percent. But those cells are made of single-crystal silicon, the same stuff that goes into computer chips. It's a good photovoltaic material, but it's expensive to grow.

Seeking an alternative, Mallouk has developed an inexpensive material that combines dye molecules with nanoparticles of titanium dioxide ("the stuff that's in white paint, and sunscreen—it's real cheap stuff"). Right now he's getting only about five percent efficiency with this composite, but he thinks it has potential to do significantly better. produce as high as 18 percent efficiency. He hopes to find ways to combine this cheaper material with the more efficient silicon in a composite cell that is both cheap and efficient. To do so, he's working with Greg Barber, an engineer at Penn State's Materials Research Institute who specializes in photovoltaic systems.

Another approach that Mallouk is investigating, with materials scientist Joan Redwing, involves a method for growing nanoscale wires of single-crystal silicon. Strung together in an array, he says, these tiny wires could conceivably accumulate enough voltage from sunlight to split water. "That's at a level of engineering we think we know how to do," he adds. "But first we need to clean up the growth process."

A third avenue that Mallouk and his students have long been pursuing bypasses electricity altogether, creating hydrogen and oxygen directly from water using only sunlight and a photocatalyst.

Call it artificial photosynthesis: You find a compound such as ruthenium trisbipyridine—"Ru-bipy" to chemists—that is energized by sunlight. You suspend it in an aqueous solution, along with a semiconducting material that is doped, or treated, with a catalyst. When sunlight hits, the electrons given off by the Ru-bipy are taken up by the semiconductor and—spurred by the catalyst—they join with hydrogen ions already present in the water to form hydrogen gas. Meanwhile, a second catalyst pulls electrons from adjacent water molecules, generating oxygen molecules and hydrogen ions. The hydrogen ions float off to further the cycle.

For this chain to play out smoothly, everything depends on having the right materials: an initial compound that gives off enough energy, a semiconductor that will hold up under water, and a catalyst that will drive the necessary reaction at a fast enough rate. And, says Mallouk, the catalysts need to be sequestered in such a way as to prevent them from contacting both products of the reaction (hydrogen and oxygen molecules). "A good catalyst for one reaction, such as water splitting, is also a good catalyst for the reverse reaction," he explains. "It is important to prevent that reverse reaction from happening, because it would convert all the stored energy into heat."

So far, Mallouk says, no one has pulled it off. After years of experiment, "We think we have components now that are viable," he adds, "but we haven't actually assembled them."

Warren Gretz (DOE/NREL)

A set of bio-reactors used for photobiological hydrogen production by the green alga, Chlamydomonas Reinhardtii.

The power of green

Hydrogen is also produced by natural photosynthesis. Biologists know that certain species of green algae and photosynthetic bacteria can make hydrogen using sunlight. Engineers are currently working on adapting this process by growing algae in bioreactors. As of yet, though, the conversion efficiency of sunlight to hydrogen is only about one percent. At that rate, the land and water requirements for growing algae would be prohibitive.

A green option that avoids the space problem is fermentation, which works by introducing hydrogen-producing bacteria-like Clostridia into water spiked with organic matter for it to feed on.

A team headed by Bruce Logan, Kappe professor of environmental engineering and director of the Penn State Hydrogen Energy Center, has successfully demonstrated fermentation using wastewater samples from several Pennsylvania food-processing plants. For their catalyst, the Logan team used ordinary garden soil that had been heat-treated to kill all the bacteria it contained except hydrogen-producing spores. When the spores were introduced to the wastewater, they began to grow, feeding on the organic material in the water and producing a biogas of 60 percent hydrogen in the headspace of the test flasks. In a second stage, Logan's students added another type of bacteria to the same water, which generated methane while consuming the leftovers.

"Using this continuous fermentation process, we can strip nearly all of the energy out of the wastewater," said Steven Van Ginkel, the doctoral student who conducted the tests. In addition, the fermentation process acts as wastewater treatment, substantially removing the need for costly aeration, Logan says.

The method holds promise, he notes, but is not yet efficient. Penn State colleagues John Regan in civil engineering and Mark Guiltinan in horticulture have embarked with Logan on a project to genetically engineer a Clostridium acetobutylicum strain that will produce more hydrogen.

Meanwhile, there are still other ways to tap the energy contained in biomass. Wood chips and agricultural waste can be converted via the same gasification techniques used to extract hydrogen from natural gas and coal. These techniques can be adapted to convert biofuels, like alcohol made from corn. Researchers— including Chunshan Song, professor of energy and geo-environmental engineering at Penn State—are working on developing better catalysts for these reactions.

Think global, act local?

"Not all hydrogen will be produced in one way," Logan told the audience gathered at University Park last fall for Hydrogen Day. "It will depend on where you live—how much sun, wind, and biomass are around." Nuclear power will also likely play a role in generating the necessary electricity. "We have to look at all our existing resources," Logan said, "and at what new technologies may emerge along the way."

Warren Gretz (DOE/NREL)

A 270-kilowatt wind turbine with advanced airfoils.

Mallouk chaired a Department of Energy panel last spring that was charged with outlining the technological obstacles to a hydrogen economy. Though he agrees in principal with Logan's assessment, he cautions, "To make hydrogen efficiently on a large scale, to avoid runaway global warming, we will ultimately need solar. Nuclear, biomass, wind, hydroelectric—they don't have enough capacity to make a dent in global energy needs. With solar, there's an unlimited supply."

The real problem, Mallouk says, is cost. And that's a problem that only grows tougher beyond our borders—borders which, when it comes to energy solutions, are increasingly permeable.

"Even if we in the U.S. can learn to sequester carbon, or subsidize solar to keep the environment clean," he says, "there are plenty of developing countries that cannot afford to do this. To make a successful transition, we will need to develop cost-efficient solutions for the rest of the world."

A fuel cell that runs on wastewater

What's even better than a fuel cell that runs on hydrogen? How about a fuel cell that runs on wastewater? Bruce Logan has not only dreamed of such a device. He's built one, and shown that it works.

For Logan, the Kappe professor of environmental engineering at Penn State, the idea came naturally. "All living things oxidize organic matter," he explains. "They eat stuff and their bodies burn it to make energy." It's the same as what happens in a conventional fuel cell, when incoming hydrogen is split into protons and electrons.

To make a microbial fuel cell, Logan continues, "you take bacteria, give it food but no oxygen, and add two conductive electrodes, an anode and a cathode. The bacteria oxidize the organic material, and transfer electrons to the anode," or negative electrode. Then the electrons flow from the anode through a wire to the cathode, "and you have current," he says. On the cathode side, the electrons recombine with the protons and with oxygen to form water.

Other researchers have shown that microbial fuel cells can produce electricity from organic material, he adds, but always using glucose, or other high-energy carbodydrates. "We showed that you can do it with any biodegradable material." Even the wastewater that's flushed down drains and toilets.

Logan's single-chambered cell, a Plexiglass cylinder the size of a soda can, houses eight graphite rods which function as anodes, providing plenty of surface area for bacteria to attach. In the center is the cathode, protected by a hollow plastic tube whose ends are open to the air.

In a trial run early last year, domestic wastewater skimmed from the settling pond of a local sewage treatment plant was pumped into the cell. Bacteria already present in the water, feeding on the organic matter also present, produced a tiny but measurable amount of electricity: from 10 to 50 milliwatts per square meter of electrode surface. Subsequent modifications, including removing the platinum catalyst on the anode—"If you have bacteria, you don't need platinum there," Logan explains—have both made the device much cheaper and boosted the power of newer devices to 494 milliwatts, enough to power a small fan. Logan's goal is 1,000 milliwatts per square meter using wastewater, a goal they have already exceeded using sugar.

The real beauty of the MFC, however, is that while it produces electricity, it also cleans the wastewater it uses. As Logan explains it, the air flow into the cathode tube causes oxidation, providing up to 80 percent of the cleaning effect normally accomplished by aeration. Since four to five percent of all U.S. electricity is used to treat wastewater, the potential savings are huge.

Last month, Logan and collaborators at Penn State and Ion Power, Inc. unveiled still another twist. By applying a small electrical current to boost the action of the bacteria in a microbial fuel cell, they reconfigured the cell to produce not electricity from wastewater, but hydrogen. Significantly, the rate of production was four times higher than that achievable by standard fermentation.

"We can theoretically use our MFC to obtain high yields of hydrogen from any biodegradable, dissolved, organic matter—human, agricultural, or industrial wastewater—and simultaneously clean the wastewater," Logan said.

"This has implications not just for the hydrogen economy," he adds. "One billion people in the world lack sanitation. Even if somebody built them a wastewater treatment plant, they couldn't afford to keep it running. But if a wastewater treatment plant can be a power plant—that's a potential paradigm shift."

—David Pacchioli

What form fits?

Finding the right storage material may be the toughest challenge.

The light and fluffy carbon material in Peter Eklund's lab has nearly 20,000 square feet of surface area crammed into each half-teaspoon worth.

"It has lots of internal spaces. When you think in terms of football fields, you realize how much space we're talking about." A football field, he notes, is about 32,000 square feet.

Courtesy Peter Eklund

Arc apparatus used in Peter Eklund's laboratory at Penn State for creating high-surface-area nanocarbons for hydrogen storage applications.

Within the nooks and crannies covering that carbon surface, Eklund, professor of physics at Penn State, is trying to "stick" as many hydrogen molecules as possible. His goal is to create a hydrogen-rich solid that could serve as a fuel tank for hydrogen-powered cars.

What might this fuel tank of the future look like? "Sort of like your water purifier cartridge but bigger — a big can filled with fluffy stuff," he says.

The push for hydrogen

In 2003, shortly after President Bush announced his hydrogen energy initiative, the Department of Energy challenged researchers across the country to develop innovative ways to store hydrogen aboard cars. At first glance, the DOE goal might not seem too hard to achieve: the storage system has to pack enough fuel to give the car a 300-mile driving range without infringing on passenger or cargo space. These are the basic standards we expect from our gasoline-powered cars.

The problem, explains Eklund, is that "when it comes to energy density, gasoline blows hydrogen away." While hydrogen packs more energy per pound than gasoline — roughly three times more — it fills four times the space. To visualize: A standard 15-gallon fuel tank holds about 90 pounds of gasoline. To get the same amount of energy from hydrogen, you'd only need about 34 pounds of fuel, but holding it would take a 60-gallon tank.

Most prototype hydrogen-powered vehicles solve the problem by using high-pressure tanks. The Toyota SUV that appeared on Penn State's campus during Hydrogen Day last November carried two such tanks in its trunk, each filled at 5,000 pounds per square inch. But safety and space remain significant concerns, says Eklund. Even tanks of compressed hydrogen are big and bulky. And, "if you puncture one of those compressed tanks, you release a lot of gas in a hurry."

Other hydrogen-powered cars, like the newest BMW model, store hydrogen as a liquid in super-cooled tanks nestled near the driver's seat. Cooling the hydrogen increases its density, but a tremendous amount of energy is required both to keep the tanks cold and, when needed, to turn the liquid back into a gas that can be delivered to an engine or fuel cell.

While some researchers are working on tanks that will safely hold both gas and liquid hydrogen at pressures up to 10,000 pounds per square inch, "we're reaching the technological limits of gas and liquid storage" of hydrogen, says Angela Lueking, assistant professor of energy and geo-environmental engineering at Penn State. "But we're just scraping the surface of what we can do with solid state."

Football fields and cages

Eklund's "high surface area carbon material," as he calls it, is just one type of solid that could potentially store significant amounts of hydrogen. Other candidates include carbon nanotubes, lightweight metals, and silicon structures. The key will be finding the one that is cheap, lightweight, and capable of storing and releasing hydrogen at convenient temperatures and pressures.

Eklund's research group spent years trying to store hydrogen inside carbon nanotubes — porous rolls of carbon, each a fraction of the diameter of a strand of hair. "But we found that carbon nanotubes could only absorb hydrogen at very cold temperatures," he reports. "We couldn't make it work at higher temperatures.—

The fluffy, high surface area carbons that Eklund and Penn State collaborators Hank Foley, Mike Chung and Vin Crespi are working with now might solve the problem. That's partly because of the unique surface structure. It looks disorganized and random, "but it has a local order — five or six hexagons of carbon lined up next to each other, and then a break or a seam, and then another group of hexagons." A weak physical attraction, called a van der Waals force, holds the hydrogen on the surface of the carbon. Adding a small amount of a lightweight metal like boron to the surface might increase the attraction. "We're trying to come up with ways to increase what's called the binding energy of the material. If we can do that, more hydrogen will stick to the surface at higher temperatures," says Eklund. "That's our goal, but we don't know if we can reach it."

Eklund is also looking at structures he calls "hydrogen cage" materials. "You can create a cage with a metal oxide or silicon," he explains. "At room temperature, hydrogen molecules can't fit into the cage. But if you heat the system, the openings in the material expand, and you can force the hydrogen molecules inside." Cooling the system causes the openings to shrink, trapping the hydrogen until it is needed.

Sponges

If you steep certain metals in a flow of hydrogen gas, the metal will gradually suck the hydrogen into its lattice structure, much like a sponge absorbs water. "It's primarily a chemical reaction," explains Digby Macdonald, distinguished professor of materials science and engineering. The hydrogen molecules break up and dissolve into the metal and may then react with the metal to form tight ionic bonds. The resulting solid is called a metal hydride.

Metal hydrides could potentially hold more hydrogen than any other solid storage system, up to 12 percent by weight. But metal hydrides tend to be heavy, and it often takes a lot of energy and very high temperatures to break those ionic bonds to release the hydrogen. "Once you get hydrogen into a solid, you have to be able to get it out," Macdonald explains. The system must be reversible, or it's not practical."

Macdonald is part of a research team that is focusing on boron, a silvery solid at room temperature that has properties of metals and non-metals alike. Boron is lighter than carbon, and "with the possible exception of carbon," it combines with hydrogen in more ways than any other element on the periodic table, forming chains, sheets, and cages—structures that are known collectively as boranes. Boranes, Macdonald says, could hold more hydrogen than any other kinds of hydride, and they could release the hydrogen at close to room temperature.

Doorways

Courtesy J.K. Johnson, University of Pittsburgh

Cartoon shows carbon nanotubes "doped" with clusters of metal. Hydrogen gas is catalyzed by the metal to stick in the nanotubes' honeycomb structures.

Lueking is studying special kinds of carbon nanotubes that are covered with clusters of metal. "The metals act like doorways, letting the hydrogen in," she explains. Some of the hydrogen is absorbed by the metals to form metal hydrides, but most of it leaks onto the surface of the nanotubes and sticks in the nanotubes' honeycomb structures.

By themselves, carbon nanotubes absorb hydrogen at extremely low temperatures, too low to be practical, says Lueking. But adding metals to the system significantly increases the temperature at which the hydrogen is absorbed. "The temperature depends on the type of metal. Right now, we're using platinum as a model because it's well characterized—we know a lot about its properties. But platinum is heavy, so we hope to apply what we learn to lighter metals like nickel and magnesium." Ultimately, the goal is to use as little metal as possible and channel most of the hydrogen onto the surface of the carbon nanotubes.

One of the problems with nanotubes, however, is cost, says Lueking. A little over two pounds of the material sells for about $50,000.

Lueking and her graduate students are also examining alternative types of carbon — graphite and coal, for example. Graphite has already been shown to absorb hydrogen when combined with lightweight metals, she notes. The structure of anthracite coal is very similar to graphite and could yield the same results.

"This is a first step in exploring cheaper, natural carbon materials."

Driving ahead

So far, however, the only storage systems that have met the DOE targets are compressed tanks of gas and liquid. A 2004 report by the American Physical Society concluded that even the most promising solid-storage technologies are still several breakthroughs away from practical use.

"It's a matter of finding the right material with the right physical properties and figuring out how to make lots of it," says Eklund. "There will definitely be a market for that material."

—Dana Bauer

Peter Eklund, Ph.D., is professor of physics and materials science in the Eberly College of Science; pce3@psu.edu. Digby MacDonald, Ph.D., is distinguished professor of materials science and engineering in the College of Earth and Mineral Sciences; ddm2@psu.edu. Angela Lueking, Ph.D., is assistant professor of energy and geo-environmental engineering in the College of Earth and Mineral Sciences; adl11@psu.edu. Eklund and MacDonald have funding from the Department of Energy's Hydrogen Center of Excellence Program for their research. Lueking's research is funded by Penn State's Institutes for the Environment and the Department of Energy's Consortium of Premium Carbon Products from Coal.

The race is on for zero emissions

Can hydrogen-based transportation make the leap from vision to reality? Experts believe success depends, in part, on whether vehicle technology and fueling infrastructure grow at the same rate and can present consumers with a convenient, appealing alternative to fossil-fuel transportation.

Tom Brewster (DOE/NREL)

The automobile industry is racing towards zero emissions. This Honda model is ready for a test drive in Palm Springs, California.

In other words, companies must offer consumers competitively-priced hydrogen-powered cars and hydrogen fuel must be available at filling stations across the country. Is such research and development cooperation possible or a pipe-dream?

In a new twist on the familiar chicken-and-the-egg question, the hydrogen conundrum can be summed up as "Which comes first? The car or the station to fuel it?" Energy companies are not likely to spend money designing infrastructure unless hydrogen cars are available, and automobile manufacturers are unlikely to build cars without fueling stations.

While industry experts haven't solved this riddle yet, most agree that hybrid vehicles will be a first step towards a widespread adoption of hydrogen transportation. They gathered at Penn State's second annual Hydrogen Day last October to discuss the alternative engine models currently being designed.

Most carmakers are experimenting with two types of hybrids: mechanical and nonmechanical. Both versions use an on-board energy source—internal combustion engines in mechanical types and fuel cells in nonmechanical models—to generate electrical power. While hybrids have far fewer emissions than all-gasoline cars, the ultimate goal is to create a zero-emissions vehicle.

Coming soon to a showroom near you? A roundup of the hybrid engines vying to replace your old gas-guzzler

Gasoline hybrid vehicle:

This concept was first introduced to the American market in 2000. The 2005 Honda Civic Hybrid uses an efficient gasoline engine with a light-weight, high-output electric motor. The electric motor is used during startup; the motor combines power with the engine during normal driving and acceleration; the battery of the electric motor charges during deceleration and the engine automatically shuts off during stops.

Courtesy Joel Anstrom

Toyota's latest fuel cell hybrid vehicle emits no exhaust.

Fuel cell hybrid vehicle:

Toyota's latest fuel cell hybrid vehicle incorporates fuel cells and a battery to release electrical power on demand. The fuel cells require a steady supply of hydrogen to operate. And—similar to the gasoline hybrid—the car's own energy is used to recharge the batteries for startup and acceleration. The first market-ready FCHV was delivered by Toyota to the University of California in December, 2002. Toyota believes "this is the first step in a plan to establish fuel cell partnerships with government, business, and universities."

Hydrogen Internal Combustion Engine (H2-ICE):

This internal combustion engine runs on hydrogen. The vehicle stores the compressed gaseous hydrogen in three tanks, and a supercharger increases the efficiency of the engine. It burns fuel more readily than a gasoline engine and produces nearly no pollutants. Matthew Younkins from Ford described Ford's strategy to use the Ford Focus H2-ICE as a technological springboard to fuel cell vehicles. "The H2-ICE is likely to stimulate the hydrogen economy and encourage infrastructure research and development," he said. Ford H2-ICE models are expected to hit showrooms by 2010.

Hydrogen fuel cell vehicle:

This zero-emission vehicle is the ultimate goal of carmakers. The fuel cells combine oxygen from the air with hydrogen from the fuel tank to produce electricity. The only byproducts are heat and water. After years of effort, many companies are now testing models of fuel cell cars: DaimlerChrysler, General Motors, Nissan, Honda, Toyota, Hyundai, Volkswagen, and Ford.

—Emily Wiley

An infinite charge

Fuel cell chemistry is a simple dance.
The trick is to make it cheaper.

The engine of the future is as quiet as a card game. There's no ignition. No exhaust smoke. No knee-trembling rumble or skull-penetrating roar.

Matt Stiveson (DOE/NREL)

Stacks of PEM fuel cells. The large unit produces 5 kilowatts of electricity, enough to power a house. The smaller stacks produce 25 and 30 watts.

In fact, a fuel cell is not an engine at all: It's an electrochemical device. Like a battery, a fuel cell produces power by converting the chemical energy present in a fuel and oxidizer directly into electricity. Unlike a battery, it doesn't store energy, and therefore it doesn't run down.

"It works like a battery with holes in the top and bottom," says Matthew Mench, assistant professor of mechanical engineering at Penn State. "You flow fuel and air through it and it produces a steady current. Keep the flow going and it's always charged."

The Welsh physicist Sir William Grove came up with the idea in 1839. Grove's "gas voltaic battery" reversed the well-known principle of electrolysis, or water-splitting, to create electrical current by combining water's components.

Simply put, a fuel cell produces electricity from hydrogen and oxygen. Its basic structure resembles a sandwich, with two chambers—one negative, the other positive—on either side of a thin electrolyte membrane. Hydrogen atoms flow into the fuel cell at the negative post (or anode). There, a catalyst triggers a chemical reaction that splits the atoms into their two parts, protons and electrons.

The positively charged protons stream through the membrane to the positive post (the cathode). The free electrons can't get through, however. Instead, they move out of the anode into electrical wiring, where they provide the direct current (DC) voltage that lights the lightbulb or powers the drive-train motor.

All electricity works by closing a circuit, so the electrons keep moving through the wiring and re-join the protons on the cathode side. That's where the hydrogen atoms mix and mingle with oxygen, with predictable results: water. The entire process is a simple chemical "dosey-do" that spins electrons away from their proton partners, then reels them back in to the dance.

Today's fuel cells come in several forms, distinguished by the material used for the electrolyte membrane. Alkaline fuel cells have long been used in the U.S. space program, but are expensive and easily contaminated. Direct methanol fuel cells will soon replace batteries in laptop computers and cell phones, but are too inefficient for larger applications. Solid oxide and molten carbonate fuel cells, which operate at temperatures over 600 degrees C, are being developed for large power plants for home and industry.

Inside the box

The sexiest fuel-cell application—and the one that's central to a hydrogen economy—is, the automobile. It's also, by far, the hardest one to achieve. "The system has to be compact," Mench explains. "It has to bear up under the harshest conditions—starting reliably in snow and heat." And the competition is brutal. "The internal combustion engine is a very mature technology."

The top contender for meeting this challenge is the polymer electrolyte membrane, or PEM, fuel cell. "It's basically a thin film between two plates," Mench says, hoisting an example. The electrolyte layer is a clear polymer membrane that looks a lot like plastic wrap. The PEM cell, he explains, operates at relatively low temperature—around 80 degrees C. That means it warms up quickly, and doesn't need much housing. It also converts energy efficiently enough that two stacks of about 200 cells—the size of a large suitcase—is enough to power a car.

There is, however, the cost problem. "To compete with a gasoline engine, we have to get to about $60 per kilowatt," Mench says. "Right now industry is at about $3,000." Another serious issue is durability. "We can get good performance at the beginning of operation," Mench says, "but you want it to last for the equivalent of 100,000 miles—that's about 5,000 hours of operation. And that's start-stop, freeze-thaw. Right now we're at about 1,000 to 4,000 hours for this type of operation."

A third major challenge is what Mench calls water management. "Basically a fuel cell is an electrochemical water-generating device. To conduct protons, the electrolyte has to be fully saturated with water. But you can't have too much just sitting in the system—it reduces performance. What if you park the car overnight and it freezes? You have to do something with it."

False-colored neutron image of a PEM fuel cell used to quantify the distribution of liquid water inside the cell. The red areas contain the most water, the dark blue and black areas the least. Imaging by Matthew Mench, in collaboration with Jack Brenizer and Kenan Unlu of Penn State's Radiation Science and Engineering Center.

At Penn State's Fuel Cell Dynamics and Diagnostics Laboratory, which Mench directs, "We're doing research to try to understand where exactly the water is in the system, and how it is causes damage," he says. "Then we can design the fuel cell to put the water where we want it." The Electrochemical Engine Center, directed by professor Chao-Yang Wang, also does computational modeling and experimental studies of fuel cells for automotive and portable applications.

At the Dynamics and Diagnostics lab, Mench uses sensors distributed throughout a fuel cell to measure temperature, moisture, and other factors at various points in the energy producing cycle. He is also working with professors Jack Brenizer and Kenan Unlu to use neutron imaging to visualize the movement of water inside a working cell. "It's analogous to an MRI or X-ray," Mench says. "Our goal is to take the fuel cell from what it has been—a black box—and to observe and measure its performance at as many points as possible."

Hot stuff

For materials chemist Tom Mallouk, "the fuel cell problem is simple. We have good fuel cells, but they're made of expensive materials." A PEM cell membrane, for instance, includes a few milligrams of platinum to help catalyze the electrochemical reaction. Add that up for 200 cells and it comes to about 150 grams. When it comes to breaking into the automobile market, that little bit of precious metal is cost-prohibitive. "Cars are sold by the pound," Mallouk says. "The price of a car is less, per pound, than the price of hamburger. You can't add tens of thousands of dollars to that."

There are several ways to cut cost, he adds. One alternative is to build a fuel cell that runs hotter. "Any reactive catalyst works better when you jack up the temperature." At higher temperatures, the polymer membrane would require far less platinum to do its job. Take it high enough, Mallouk says, and you could substitute nickel, a less efficient—but much cheaper—catalyst.

Unfortunately, raising the temperature also runs the risk of material failure. The current polymer membranes, Mallouk explains, "are flexible, compliant, good proton conductors, but they only work when swelled with liquid water. If the water is boiled away, they won't work. So right now the big push is for fuel cells that run hotter but still below the temperature where polymer membranes lose all their water, about 200 degrees C."

An alternate approach, he says, would be to find a completely new material, something that can do what membranes do—conduct protons, hold up mechanically—at well above the boiling point. "If you could make a membrane that works at 300 degrees C," Mallouk says, "the catalysis problems would go away. That's one of the things we're working on."

Mallouk's idea is to move from polymers to inorganic materials, like ceramics. "They can retain water up to 300-400 C," he says. "They contain water within their crystalline structure." Ceramics can also be good proton conductors. The problem, though, is that ceramics tend to be brittle. They lack the mechanical strength needed for a flexible membrane.

"A few years ago," Mallouk remembers, "a colleague of mine, Eugene Smotkin at the University of Puerto Rico, had the idea of making a membrane that was a composite of a metal foil and a proton-conducting polymer. Metal foil is all wrong electronically—metal is a conductor not an insulator, and it won't allow protons through—but mechanically it's strong. And actually, certain metals, like palladium alloys, would let protons through." On came the lightbulb: Why not a composite? "The foil supports this patchy layer of ceramic deposited on top of it, which in turn acts as an insulator," Mallouk explains.

"We tried this in 1998 with a real simple system, and showed that it works," he says. Since then, he and his students have been fine-tuning. "The challenge is to make the perfect inorganic material for that thin film on top of the foil."

Help for hybrids

Serguei Lvov is also interested in making membranes that work at higher temperatures. "High temperature should improve performance," notes the professor of energy and geo-environmental engineering. "At higher temperatures the membrane can better survive impurities like carbon monoxide," which choke current fuel cells. Equally important, he says, hotter running cells are compatible with existing automotive technology.

"I think nobody now believes that a straight fuel-cell car is going to run in the near future," Lvov explains. Instead, "we're probably going to have a hybrid—consisting of a battery, a fuel cell, and a traditional heat engine." To make this combined system economical, "you need to run the fuel cell at high temperature—the automakers want 120 or even 130 degrees C." That bump in temperature, he says, makes humidity inside the cell a concern. "Below 100 degrees C, where PEM fuel cells run now, relative humidity is not a serious issue," he explains. "At 120, just a little bit makes performance drop off."

Courtesy Serguei Lvov

Scanning electron microscope (SEM) image showing morphology of composite membranes made of Nafion and titania by Serguei Lvov's research group at Penn State.

Lvov thinks he and his team may have come up with a membrane material that can stand both high temperature and low humidity. It's based on combining the proton-conductive polymer Nafion with titanium oxide, or titania—the same white powder Tom Mallouk is using to make cheaper solar cells. "Nafion is a very well-known material, very well tested, and titania is very inexpensive, and also a proton-conductive inorganic," he says. "If you put the two together you end up with a cheap composite material that is mechanically stable, and can operate at a higher temperature. And we have shown that it works in an atmosphere of as low as 25 percent relative humidity."

The discovery, he notes, was somewhat serendipitous. Lvov was directing parallel projects, one with Department of Energy support aimed at developing high-temperature fuel cells, and the other, with support from Oak Ridge National Laboratory, whose goal is understanding the basic electrochemical surface properties of titania. "I saw that people were starting to use composite materials for fuel cell membranes," he says, "and one of those composites was Nafion and silica. At the same time, I had learned enough about titania's surface properties, and the differences between it and silica, that we decided to try titania for this purpose. And it looks like we were successful." Penn State has submitted a patent on Lvov's Nafion-titania composite membrane, and Dupont has signed on to sponsor further studies.

For Lvov, one lesson is clear. "Fuel cell research is very complicated. If you want to end up with something new, you have to bring together expertise from many different areas—polymer science, inorganic materials, electrochemistry." He has assembled a team consisting of 17 Penn State researchers, along with colleagues from other universities and industry, with the hope of starting a center for developing composite membranes.

Lvov isn't leaving future success up to happy accident. "In order to advance further," he emphasizes, "we must be very deliberate."

Joel Anstrom is thinking ahead. In his view, the long term goal of the project is to reduce reliance on petroleum by introducing a hydrogen infrastructure at gas-competitive prices. Anstrom, director of Penn State's Hybrid and Hydrogen Vehicle Research Center (HHVRC) at the Pennsylvania Transportation Institute (PTI), heads the vehicle fleet and assists Bohdan Kulakowski, professor of mechanical engineering, with the fueling station. He is optimistic that Penn State's hydrogen fueling station is an interim step towards future savings and independence for American drivers. Says Anstrom, "We want to demonstrate a safe, reliable, and affordable hydrogen transportation infrastructure that can be placed at filling stations across the country."

The HHVRC team, with technical support from Collier Technologies, Inc. is converting the Penn State vans and CATA buses to run on a blend of hydrogen and compressed natural gas (HCNG). Collier has patented technology which allows engines to run on up to 40 percent hydrogen blended with natural
gas while producing very low emissions. Last October, the Collier staff converted Penn State's first van to the HCNG blend, supplying the training and conversion kits that Penn State mechanics will use to modify the remaining vehicles.

Meet HyLion

Emily Wiley

Interior of HyLion.

The single car in the fleet has different requirements. "The fuel cell car is an electric vehicle with a hydrogen fuel cell added to extend its range," explains Anstrom. "We call it HyLion." The chassis was donated to Penn State by General Motors with its original electric batteries and some controllers removed. HHVRC compiled a new battery pack and is working to develop the new controllers needed to communicate with the fueling station.

Anstrom says the new controller of HyLion will boost the 24 volt output of the fuel cell up to the 350 volt level. "The 350 volts of the battery pack are manipulated into an alternating current, much like a house current," describes Anstrom. "It propels the drive motor on the front wheels and also allows battery charging and exporting power from the car to the utilty grid."

What did the pump say to the tank?

So how will the Penn State fleet feed its need for fuel? Imagine a conversation between the fuel tank and the filling pump. Unlike a gasoline station, the hydrogen dispensor actually communicates with the vehicles and fueling occurs in a completely sealed system.

The dispenser nozzle is designed to flow fuel only if properly connected and sealed to the car nozzle. It is impossible to release hydrogen from the dispenser nozzle itself, Anstrom says. An electric connector, much like a computer cable, transmits measurements of tank pressure, temperature, and capacity from the car to the station. Control signals allow the station and vehicle to "hand shake" to confirm the start and end of fueling operations. If the proper signals are received, the station will fill the car's tank with hydrogen. Minor faults will cause filling at a slower rate, and major errors will prevent filling altogether.

Sound complicated? Anstrom says it's as easy as gasoline fueling. The driver simply attaches the station's electrical connector to the car to establish initial communication. Next, the hose nozzle is placed over the vehicle receptacle. (A rotating handle on the nozzle turns 180 degrees to create a seal between the station and the car.) Once the driver enters a secure PIN number, the station finishes the fill under computer control. After filling, the nozzle and electrical connector are removed and stored. Eventually, hydrogen dispensers will use wireless communication with the car to eliminate the cable.

Fool-proof fueling

"Although the station is automated to control the process and detect problems, the development team has taken some extra safety precautions," says Anstrom. For instance, the filling hose is designed to detach and seal in the event that the driver speeds away while still attached to the station. ("We have to anticipate human error before it occurs," notes Anstrom.) Extra electrical grounding will prevent static discharges, and the on-campus vehicle storage buildings have hydrogen leak detectors and are designed with an automatic venting system.

Courtesy Joel Anstrom

Joel Anstrom inspects part of Penn State's vehicle fleet.

The vehicle demonstration is intended to place substantial demand on the new fueling station, Anstrom says. Daily fueling at the site must consume over 40 percent of the hydrogen to prevent frequent shutdown and startup cycles of the hydrogen reformer. According to Anstrom, PTI's ultimate plan is to fuel the HyLion twice daily, along with the three buses and one or two of the vans. PTI will operate the HyLion on campus; CATA will run the buses on its University Park Loop route; and OPP will operate the vans on campus to perform building maintenance.

Coast-to-coast hydrogen

Anstrom says Penn State's local demonstration is part of a larger scale long-term plan to link to other local hydrogen fueling stations in Washington, D.C., Pennsylvania, Ohio, and Michigan. Stations in these locations currently run vehicles within limited ranges, but the dream is to create a highway from Detroit to D.C., much like the California Hydrogen Highway.

—Emily Wiley

Joel Anstrom, Ph.D., is director of Penn State's Hybrid and Hydrogen Vehicle Research Center at the Pennsylvania Transportation Institute. He can be reached at jra2@psu.edu.

The price of power

Can hydrogen stack up to the competition?
A conversation with Tim Considine

There's an economist at the hydrogen energy party and he's not afraid to speak his mind. "I hate to sound like a pessimist," says Tim Considine, professor of natural resource economics at Penn State. "But the simple fact is hydrogen is not economical, and it's unlikely to be for quite some time."

What's in the way? According to Considine, production costs, major technical hurdles, and society's reluctance to pay the true cost of burning fossil fuels, to name just a few obstacles.

Emily Wiley

Can hydrogen compete at the pump?

According to a 2004 report from the National Academy of Engineering, "the vision of the hydrogen economy is based on the expectation that hydrogen can be produced from domestic energy sources in a manner that is affordable and environmentally benign," and that "applications using hydrogen—fuel cell vehicles, for example—can gain market share in competition with the alternatives."

The conclusion of the committee that authored the report? A transition to a hydrogen economy is, at best, decades away.

Considine agrees. "We have a long way to go."

Former associate editor Dana Bauer sat down with Tim Considine to learn more about the direction—and challenges—of hydrogen research.

Q: Gas is cheap. How can hydrogen compete?

A: You can make a case that if one were to internalize all the external effects from burning gasoline — these might be air pollution, health effects, the amount of money that we're spending directly and indirectly on the military to protect world oil lands — one could calculate that the true social cost of oil is not $30 to $40 a barrel, it's at least $100 a barrel.

So, if you believe that, the corrective policy is to put a tax on gasoline. If the social cost of oil is $50 a barrel, say, you divide that by 42 gallons in a barrel, that's more than a $1 tax per gallon of gasoline. But tell me what politician would be willing to put a tax of a dollar on gasoline?

So that's the essence of the problem. We're not paying the true cost of gasoline. The point is that hydrogen and alternative fuels have to compete in that type of market.

Also there is competition from the good old internal combustion engine. Don't rule it out. Automakers have been improving the internal combustion engine on a steady basis over the past ten years and it's likely to improve even further both in terms of fuel efficiency and power output.

Q: What are the biggest challenges facing hydrogen research?

A: Right now, producing hydrogen is expensive and energy intensive. It takes about six gallons of gasoline to make and compress a little over two pounds of hydrogen, which carries about the same amount of energy as a gallon of gasoline.

The biggest producer of hydrogen is the oil industry. Coal and natural gas are alternative ways to fuel hydrogen production, but at some point we're going to have to go nuclear. We'll run out of oil and natural gas.

Researchers also need to develop efficient and affordable fuel cell technologies and a safe and economical means of storing hydrogen aboard vehicles.

Q: Will consumers go for hydrogen-powered vehicles?

A: What do consumers want in vehicles? They want safety and they want space. Granted, there's a segment of the population that's happy driving small cars, but it's a small segment. Most of the market, more than 50 percent, is after space and safety.

The other thing is that cars are becoming electronic platforms for gadgets — DVD players, stereos. Cars are becoming power plants and they have more creature comfort features that consume energy. That's a real demand on the engine to produce power.

Also, think about this: You have a hydrogen vehicle and someone comes along and says, 'Hey, we can sell you a Chevy Suburban that seats eight and gets 40 miles a gallon.' Don't rule it out. You could see a dramatic increase in fuel economy among the SUVs. Right now there's no great incentive, but the technology is there to do it.

Leslie Eudy (DOE/NREL)

What will it take for consumers to purchase hydrogen vehicles?

Q: Will automakers make hydrogen vehicles?

A: Automakers are risk averse. Increasingly, these companies are in the service business. You've seen the warranties go up in the past 10 years. They all have to have solid service and repair networks. So when you're talking about switching to a new kind of vehicle, you're talking about a radical change in the whole service infrastructure. Making these changes is a huge logistical challenge for the automakers. It's capital intensive. It has to evolve. You're not going to see these changes happen very quickly.

Q: Are hybrid vehicles a good way to test the waters?

A: Automakers are learning about that technology, too. When they build these hybrids, they don't know how long they're going to last. The engineers can estimate, but you don't really know until consumers start to use them and get them into the repair network.

Most of the major car companies have hybrids on the market. You see more hybrids in Japan. California is a good market for hybrids. Some of the car companies are talking about bringing hydrogen cars to market in the 2010 to 2020 time frame. They'd be sort of sliding into the same market that hybrids are in now.

Q: Why is the idea of a hydrogen economy so popular? What are the steps to getting there?

A: I'm focusing on transportation, because that seems to be where the big push for hydrogen is. One of my main motivations is that scientists, engineers, and politicians see the great promise of hydrogen as a clean fuel, no pollution. That's the nirvana that everyone's looking for.

Politically, it's very attractive. A lot of areas in the country have real air quality problems. Something has to be done. Hydrogen may be a solution. It's just going to take a while.

There is now a cottage hydrogen industry that's feeding off of federal support and most of the major automakers are conducting research and development on hydrogen fuel cells. These programs will continue.

And there's a legitimate case for research and development. There could be a dramatic breakthrough in fuel cell operation. There have already been significant reductions in fuel cell operating costs because material scientists have been able to reduce the amount of platinum used in fuel cell catalysts. There could be other similar materials science based innovations — special membranes to store hydrogen at a higher density, for example.

So technology changes and advances and you don't know when it's going to happen. But it's a race because conventional technology is getting more efficient as well.

—Dana Bauer

Tim Considine, Ph.D., is professor of natural resource economics in the College of Earth and Mineral Sciences; cpw@psu.edu.

Pennsylvania seeks tomorrow's energy today

Pennsylvania is deeply connected to all things energy, believes state native and Department of Environmental Protection Secretary Kathleen McGinty. "We have a rich energy history to draw upon, and the nation is looking to us to help build energy's future," McGinty asserted at Penn State's second annual Hydrogen Day in October.

In her keynote speech, McGinty dramatically demonstrated the impact of clean energy on the physical world by holding up two leaves of the same species—one grown in ambient air and the other in a plastic tent of ozone-filtered air. The leaf untouched by air pollution was noticeably larger and healthier and served as a visual reminder of pollution's harmful effects.

"Our nation has a dangerous dependency on unreliable fuel imports," states McGinty. "We need to reinforce the greatness of the United States by answering our rising energy needs with a clean solution."

Emily Wiley

Penn State teamed with Colier Technologies, Inc. to create this fuel cell.

At the state level, Governor Ed Rendell's administration recently launched the Pennsylvania Hydrogen and Fuel Cell Consortium. Its purpose: to build support for the hydrogen economy by encouraging partnerships among government, academia, and industry related to energy technology. Consortium partners include the U.S. Department of Energy (DOE), Franklin Fuel Cells, Inc., and Air Products and Chemicals, Inc., among others. The partners have diverse experience in basic research and product development of clean and efficient energy conversion technology. For example, Siemens Westinghouse is working with the DOE to develop solid oxide fuel cells and expects to have its first commercial product available in 2008. Other partners are working on hydrogen fuel infrastructures, hydrogen purifiers, and metal catalysts. There are currently six companies listed as members of the Consortium, and membership continues to grow with each meeting.

McGinty thinks this is a step in the right direction, describing the project as "truly inspiring." The development of hydrogen fuel is such an immense research endeavor that no single organization can progress alone. "Industry partners and academic institutions may be competitors at some levels, but at this critical stage, they work together,v she notes. "There is a rich set of collaboration on display here in Pennsylvania."

Pennsylvania's plan for the years ahead, says McGinty, is to secure federal grant money for clean energy initiatives and produce energy closer to home. "We are the first state in the nation to put our own money where our mouth is," she declares with satisfaction. "We are on our way to producing 20 percent of all state energy needs from clean energy."

The Commonwealth has also received national recognition for a waste coal production power plant in Indiana County and has seen a significant increase in the deployment of wind energy across the state.

As a result of Pennsylvania's initiatives, advanced energy standards have become a bipartisan effort across the country.

McGinty said hydrogen-powered vehicles are not just wishful thinking, but a realistic 21st century solution. "Clean energy is our future as fossil fuel energy has been our past," she said. "And Penn State is at the cutting edge."

—Emily Wiley

SIDEBAR

Park to the Future

"Energy is the most critical challenge facing humanity." -Bruce Logan, Kappe Professor of Environmental Engineering at Penn State, elaborates on this quote by Nobel Laureate Richard Smalley during Hydrogen Day 2004.